Camera system and display device

ABSTRACT

The invention relates to a camera system and to a display device for displaying images recorded by the camera system. The camera system comprises a camera ( 1 ) provided with an optics system ( 2 ) and a photosensitive image surface ( 3 ) disposed near the optics symmetrically relative to its optic axis, the image refracted by the optics being projected onto said image surface. The photosensitive image surface is a concave spherical surface whose center of curvature is at the focal point of the optics.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a camera system as defined in thepreamble claim 1.

(2) Description of the Related Art

Photography was invented in the early part of the 19^(th) century.Fairly soon, silver halides (AgBr, AgCl) were distinguished from thespectrum of light-sensitive materials as they were found to belight-sensitive when dispersed in gelatin. The dispersion was spread ona glass plate, which formed the photosensitive projection surface of thecamera. The glass plate was a straight plate, and an optical system wasdeveloped which focused the image onto the plate even through apertureslarger than a pinprick.

The glass plate was followed by the film, the film was followed by thevidicon, and the vidicon was followed by the digital matrix. However,the image plane still remains a plane both in cameras for still picturesand those for moving pictures. In azimuthal projection, the illuminationon the projection surface is proportional to the square of the angle ofdeflection as measured from the optical axis:I=(L cos⁴ φ)/4f(1+m)²

-   -   where    -   I is intensity at image plane,    -   L is luminance at target,    -   φ is the angle of a focus-originated radius to the optical axis,    -   f is the aperture number, and    -   m is the conversion factor.

Especially in the case of wide-angle optics, problems are encountered inrespect of uniformity of illumination in the image area. Further,wide-angle images with an angular field of the lens exceeding 100° aredifficult to accomplish without substantial distortion of straightlines.

In prior art, both of the above-mentioned errors have been corrected byway of digital image processing.

The object of the invention is to eliminate the drawbacks referred toabove.

DETAILED DESCRIPTION OF THE INVENTION

A specific object of the invention is to disclose a camera system and acorresponding display device that will make it possible to produce awide-angle image in which illumination is uniform over the entire imagearea and no lines in the image area are distorted.

As for the features characteristic of the camera and display device ofthe invention, reference is made to the claims.

The camera system of the invention comprises a camera provided with anoptics system and a photosensitive image surface disposed in thevicinity of the optics system symmetrically relative to its optic axis,the image of the target refracted by the optics being projected ontosaid image surface.

According to the invention, the photosensitive image surface is aconcave spherical surface whose center of curvature is at the focus ofthe optics. The camera of the invention projects the image onto theconcave, focus-centered spherical surface, which functions as a lightdetector and may consist of light-sensitive detecting elements.

The camera system of the invention does not exhibit any anisotropy orgeometric distortion, which are typical of conventional photographictechniques. The invention makes it possible to implement different focaldistances up to a 180° observation angle.

The invention has the advantage that, when a normal focal distance isused, with a 60° angular field of the lens, the cosine error is avoided.Therefore, the isotropy of the image in respect of illumination issignificantly better than in prior-art cameras. This is important invarious image analysis applications in which the reflection density andcolor are used as a basis for making inferences about the target beinganalyzed.

When short focal distances (up to a 180° recording angle) are used, theinvention has the advantage of eliminating the geometric distortionstypical of current optical systems. When pictures are to be printedand/or displayed using traditional planar display surfaces, suitablerectangular undistorted areas can be cut off from the image by usingappropriate software. When a display device according to the inventionis used in which the display surface is a concave spherical surface, nogeometric distortions appear.

When long focal distances are used, the visual effect that shortens therelative distances is eliminated.

In an optical sense, projecting the image onto a spherical surface is aless demanding task than conventional planar projection. Therefore, thecost of manufacturing an optical equipment free of aberrations for thesystem of the invention is lower than in the case of conventionaloptics.

In an embodiment of the camera system, the photosensitive image surfaceconsists of a matrix of individual light-sensitive detecting elements,such as CCD elements.

In an embodiment of the camera system, the number of detecting elementsis of the order of 100000 or more.

In an embodiment of the camera system, the number of detecting elementshas been so chosen that, in order to achieve a reasonable image quality,the number is of the order of 10⁴−3×10⁴, to achieve a good imagequality, of the order of 10⁶−2×10⁶, or to achieve a perfect imagequality, of the order of 10⁸.

In an embodiment of the camera system, the detecting elements are soarranged on the image surface that their density is at a maximum on theprincipal axis and diminishes from the principal axis toward the edgezones.

In an embodiment of the camera system, the density distribution of thedetecting elements on the image surface is consistent with the function:

${{I(r)} = {I_{0}e^{- {a{(\frac{\sqrt{x^{2} + y^{2} + z^{2}}}{r_{0}})}}^{2}}}},$where

I₀ density of detecting elements at the origin (on the principal axis),

I(r)=local density of detecting elements at radius r from the origin,and

a=scaling factor.

In an embodiment of the camera system, the detecting elements in thehigh-resolution area near the optic axis are so arranged that the pointspread function (PSF) produced by the optics integrates over severaldetecting elements to prevent aliasing.

In an embodiment of the camera system, the optics are of a type using aso-called normal focal distance and the image surface is a sphericalcalotte with a recording angle (α) of the order of 60°; and the cameracomprises a shutter disposed between the optics and the image surfaceand provided with an adjustable aperture.

In an embodiment of the camera system, the recording angle of the imagesurface is 180° or less.

In an embodiment of the camera system, the optics comprise a lens with ashort focal distance, such as a so-called fish-eye lens; the imagesurface is of a hemispherical shape and the recording angle is 180°, sothat the camera is of a semispace recording type.

In an embodiment of the camera system, the camera is a digital camerawhich comprises means for digitization of the signals received from thedetecting elements and means for transferring the digitized images to acomputer. The image can be processed, transferred and printed in adigital form. The images can be displayed using a spherical surfacedisplay as mentioned above or conventional display devices. They canalso be printed in an undistorted form on paper using image printers.

In an embodiment of the camera system, the camera is of a type designedto record moving pictures.

In an embodiment of the camera system, the camera is of a type designedto record still pictures.

In an embodiment of the camera system, the camera is a monitoringcamera.

In an embodiment of the camera system, the system comprises twosemispace recording cameras directed in opposite directions to therecord the whole space.

In an embodiment of the camera system, the system comprises two adjacentsemispace recording cameras directed in the same direction for therecording of a stereo image of the semispace.

According to the invention, the display surface of the display deviceused for the display of an image recorded using the above-mentionedcamera system is a concave spherical surface.

The display device has the advantage that the illumination in the imageis uniform over the entire image area and the image is geometricallyundistorted, thus requiring no corrective processing regarding theluminance level or contours of the picture.

In an embodiment of the display device, the display device is a monitor,such as a computer monitor or a television, having a screen of the shapeof a concave spherical calotte.

In an embodiment of the display device, the display surface is a wall orceiling surface of a room, onto which the image can be projected so asto allow it to be viewed simultaneously by a plurality of persons.

In an embodiment of the display device, the display device is a personaldisplay visor or the like, in which the display surface is ahemispherical display surface having its center at the focal point ofthe eye.

In an embodiment of the display device, the display visor or the likecomprises two hemispherical display surfaces having their centers at thefocal points of the eyes, one display surface for each eye for theviewing of stereo pictures.

In an embodiment of the display device, the display surface consists ofa matrix of individual picture elements.

In an embodiment of the display device, the number of picture elementsis of the order of 100,000 or more.

In an embodiment of the display device, the number of picture elementshas been so chosen that, in order to achieve a reasonable image quality,the number is of the order of 10⁴−3×10⁴, to achieve a good imagequality, of the order of 10⁶−2×10⁶, or to achieve a perfect imagequality, of the order of 10⁸.

In an embodiment of the display device, the picture elements are soarranged on the display surface that their density is at maximum on theoptic axis and diminishes from the optic axis toward the edge zones.

In an embodiment of the display device, the picture elements of thehemispherical display surface are larger in surface area in the edgezones than in the vicinity of the principal axis.

In an embodiment of the display device, the density distribution of thepicture elements on the display surface is consistent with the function:

${{I(r)} = {I_{0}e^{- {a{(\frac{\sqrt{x^{2} + y^{2} + z^{2}}}{r_{0}})}}^{2}}}},$

-   -   where    -   I₀=picture element density at the origin (on the principal        axis),    -   I(r)=local picture element density at radius r from the origin,        and    -   a=scaling factor.

In an embodiment of the display device, the picture elements areimplemented using fiber optics.

Cameras and display devices constructed according to the invention arevery well suited for use in robotics applications with a visualcapacity. As there are no line distortions, corresponding correctioncomputation is avoided. As there are no structural illuminationdifferences between the optic axis and the peripheral image areas, theinterpreting computation produces more accurate results than when atraditional camera is used. Cameras and display devices constructedaccording to the invention are also very well applicable for use insimulators in which stimuli are created artificially for the entirevisual field (e.g. flight simulator). Similarly, it is possible toproduce entertainment and computer game material that gives a person asensation of being virtually present in the situation photographed bythe camera and reproduced by the spherical display. Using a pair ofadjacent cameras, it is possible to generate a three-dimensionalperception that fills the entire field of vision.

In the following, the invention will be described in detail by the aidof a few examples of its embodiments with reference to the drawings,wherein

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a skeleton diagram of a first embodiment of the camerasystem of the invention.

FIG. 2 presents a skeleton diagram of a second embodiment of the camerasystem of the invention,

FIG. 3 presents a diagram illustrating the prevention of aliasing bymeans of the optics at points where the density of picture elements itat a maximum,

FIG. 4 presents a diagram illustrating a monitoring camera applicationof the camera system of the invention for the monitoring of a semispacein a room,

FIG. 5 presents a diagram illustrating a monitoring camera applicationof the camera system of the invention for the monitoring of the wholespace in an open area,

FIG. 6 presents a diagram of a first embodiment of the display device ofthe invention, i.e. a spherical calotte type monitor or television andan optimal viewing line for it,

FIG. 7 presents a diagram of a second embodiment of the display deviceof the invention that allows the display of images to a plurality ofviewers,

FIG. 8 presents a third embodiment of the display device of theinvention, which is a personal display device for the display of stereopictures,

FIG. 9 presents a diagram representing a fourth embodiment of thedisplay device of the invention, which is a personal display device forthe display of mono pictures.

FIG. 1 shows a camera 1 which comprises optics 2 with a so-called normalfocal distance, presented in the figure as a simple lens. The camera 1further comprises a photosensitive image surface 3, which is a concavespherical surface, onto which the optics 2 project the image of thetarget. The center of curvature of the image surface 3 is at the focalpoint of the optics 2 on the optic axis L. With a lens 2 with a normalfocal distance, a 60° recording angle is obtained, so the camera mayhave an image surface the shape of a spherical calotte. The camerafurther comprises a shutter 4 provided with an adjustable aperture anddisposed near the lens 2, between the lens 2 and the image surface 3.

The optics 2 in the camera 1 in FIG. 2 comprise a lens 5 with a shortfocal distance, a so-called fish-eye lens. The image surface 3 is of ahemispherical shape, so the camera is a semispace recording type ofcamera. The figure illustrates the projection of three targets I, I, IIIonto the hemispherical image surface. The recording angle is 180°. Thepicture of target I on the principal axis L is recorded on the imagesurface 3 on the principal axis L. Targets II and III, located onopposite sides at angles of 90°, are projected onto the edges of thehemispherical image surface.

The cameras in FIGS. 1 and 2 are preferably digital cameras capable ofboth still and moving image photography. The image surface 3 of thecamera 1 is composed of individually placed digital detecting elementsor it may be constructed using fiber optics. A reasonable image qualityis achieved using about 100 000–300 000 detecting elements on the imagesurface 3. A good image quality is achieved using about 1–2 milliondetecting elements. If perfect image quality is desired, then the numberof detecting elements should be of the order of 10⁸.

In cameras with a recording angle of 180° of the image surface 3 asillustrated in FIG. 2, which can see an entire semispace, withcorresponding display devices, the position of the optic axis Lcorresponds to the point of sharp vision in the human eye while the edgezones correspond to the less sharp peripheral vision. Therefore, thedensity of detecting elements on the image surface 3 may vary so thatthe density is at a maximum in the region of the optic axis, i.e. theresolution is high, being reduced towards the edge zones, where theresolution is lower. For example, the Gaussian detecting element densitydistribution roughly corresponds to the frequency of utilization of theinformation when the image is being viewed. Other distributions are alsopossible. A varying detecting element density is suited for use e.g. ina remote control application in which a camera according to theinvention installed on a robot photographs a real target while a personcontrolling the robot is watching the image produced by the camera,using a display device according to the invention. The distribution ofthe detecting element density on the image surface 3 may be e.g. asgiven by the following function:

${{I(r)} = {I_{0}e^{- {a{(\frac{\sqrt{x^{2} + y^{2} + z^{2}}}{r_{0}})}}^{2}}}},$

-   -   where    -   I₀=detecting element density at the origin (on the principal        axis),    -   I(r)=local detecting element density at radius r from the        origin, and    -   a=scaling factor.

If the shooting frequency of the camera is higher than half the sensorfrequency, this will result in a so-called aliasing effect, inconsequence of which, when the frequency increases, MTF, having droppedto zero, receives high positive values at higher frequencies. Especiallywhen structured objects are being photographed, this causes asubstantial deterioration of image quality. Aliasing can be avoided inthe high-resolution portions of a variable-resolution camera by using anarrangement as illustrated in FIG. 3. The point spread function PSF ofthe optics is so adapted that it will integrate over a few adjacentdetecting elements.

FIGS. 4 and 5 illustrate the use of a semispace recording camera aspresented in FIG. 2 as a wide-angle monitoring camera. Unlike previouslyknown cameras which need to be moved to scan the surroundings, a cameralike this can be fixedly and immovably mounted on the wall or ceiling ofa room as shown in FIG. 4. When used e.g. as a monitoring camera in abank, such an immovable camera is unnoticeable and difficult to detect.By using a pair of cameras looking in opposite directions as in FIG. 5,the whole open space around (2×semispace) can be monitored. Using asingle camera, a geometrically undistorted picture of the semispace isproduced by a single shot without moving the camera. Using two semispacerecording cameras directed in the same direction, it is possible toproduce stereo pictures to create a three-dimensional impression.

Pictures taken with the camera of the invention can be viewed as normalplanar copies by using a planar display or making a planar print-out. Itis also possible to construct special display devices 6 as presented inFIGS. 6–9 for the viewing of pictures taken with the camera 1. In adisplay device 6 like this, the display surface 7 on which the picturesare viewed is a concave spherical surface.

FIG. 6 presents an embodiment in which the display device 6 is amonitor, such as a computer monitor or television, whose display screenis a display surface 7 having the shape of a concave spherical calotte.For this device, a preferable viewing distance is twice the radius r ofthe spherical calotte. The optimal viewing line is indicated by a brokenline 8.

Referring to FIG. 7, in an application for a plurality of viewers, thedisplay surface 7 may also consist of a hemispherical wall or ceilingsurface in a room (omni-theater), onto which the image can be projectedfor simultaneous viewing by several persons.

FIGS. 8 and 9 present a display device 6 which is a personal displayvisor, display helmet or the like, in which the display surface 7 is ahemispherical display surface whose center is at the focal point of theeye. This device can be used e.g. for the presentation of virtualreality in entertainment and game applications and as a helmet displaye.g. for air pilots.

In FIG. 8, the display visor or the like comprises two hemisphericaldisplay surfaces 7 having their centers at the focal points of the eyes,one display surface for each eye, for the viewing of stereo pictures,producing a three-dimensional impression.

In FIG. 9, the display visor is provided with a mono display with asingle hemispherical display surface 7.

The display surface 7 in the display devices may consist of a matrix ofindividual picture elements. The number of picture elements has been sochosen that, to produce a reasonable image quality, the number is of theorder of 10⁴−3×10⁴, to produce a good image quality, of the order of10⁶−2×10⁶, or to produce a perfect image quality, of the order of 10⁸.

When the input device used is a variable-resolution camera, the displaydevice can be constructed as a variable-resolution display. In a 180°display, the peripheral areas are implemented using fewer but largerpicture elements, but so that they correspond to the high-resolutionarea in respect of image energy (=area of picture element×maximumluminance).

In a variable-resolution display device 6, the picture elements may beso arranged on the display surface 7 that their density is at a maximumon the principal axis L, diminishing from the principal axis toward theedge zones. The density distribution of the picture elements on thedisplay surface is as expressed by the function:

${{I(r)} = {I_{0}e^{- {a{(\frac{\sqrt{x^{2} + y^{2} + z^{2}}}{r_{0}})}}^{2}}}},$

-   -   where    -   I₀=picture element density at the origin (on the principal        axis),    -   I(r)=local picture element density at radius r from the origin,        and    -   a=scaling factor.

The invention is not restricted to the examples of its embodimentsdescribed above; instead, many variations are possible within the scopeof the inventive idea defined in the claims.

1. Camera system comprising a camera (1) provided with an optics system(2) and a photosensitive image surface (3) disposed near the opticssystem symmetrically relative to its optic axis (L), the image of theobject (K) refracted by the optics being projected onto the imagesurface, the photosensitive image surface (3) being a concave sphericalsurface whose center of curvature is at the focal point of the optics(2) and consisting of a matrix of individual photosensitive detectingelements, characterized in that the detecting elements are so arrangedon the image surface (3) that their density is at a maximum on the opticaxis (L) and diminishes from the optic axis toward the edge zones,characterized in that the density distribution of the detecting elementson the image surface (3) is consistent with the function:${{I(r)} = {I_{0}e^{- {a{(\frac{\sqrt{x^{2} + y^{2} + z^{2}}}{r_{0}})}}^{2}}}},$where I₀=density of detecting elements at the origin (on the opticaxis), I(r)=local density of detecting elements at radius r from theorigin, and a=scaling factor.
 2. Camera system as defined in claim 1,characterized in that photosensitive detecting elements are CCDelements.
 3. Camera system as defined in claim 1, characterized in thatthe number of detecting elements is of the order of 100000 or higher. 4.Camera system as defined in claim 3, characterized in that the number ofdetecting elements has been so chosen that, to achieve a reasonableimage quality, the number is of the order of 10⁴−3×10⁴, to achieve agood image quality, of the order of 10⁶−2×10⁶, or to achieve a perfectimage quality, of the order of 10⁸.
 5. Camera system as defined in claim1, characterized in that the optics (2) has been so arranged that, inthe high-resolution area near the optic axis (L), the point spreadfunction (PSF) produced by the optics integrates over several detectingelements to prevent aliasing.
 6. Camera system as defined in claim 1,characterized in that the optics (2) is of a type having a so-callednormal focal distance and the image surface (3) is a spherical calottewith a recording angle of the order of 60°; and that the cameracomprises a shutter (4) disposed between the optics and the imagesurface and provided with an adjustable aperture.
 7. Camera system asdefined in claim 1, characterized in that the recording angle of theimage surface (3) is 180° or less.
 8. Camera system as defined in claim1, characterized in that the optics (2) comprises a lens (5) with ashort focal distance, such as a so-called fish-eye lens; that the imagesurface (3) is of a hemispherical shape and the recording angle is 180°,the camera thus being of a semi-space recording type.
 9. Camera systemas defined in claim 1, characterized in that the camera (1) is a digitalcamera, which comprises means for digitization of the signals receivedfrom the detecting elements and means for transferring the digitizedimages to a computer.
 10. Camera system as defined in claim 1,characterized in that the camera (1) is of a type for recording movingpictures.
 11. Camera system as defined in claim 1, characterized in thatthe camera (1) is of a type for recording still pictures.
 12. Camerasystem as defined in claim 1, characterized in that the camera (1) is amonitoring camera.
 13. Camera system as defined in claim 1,characterized in that the system comprises two semi-space recordingcameras (1) directed in opposite directions for the recording of thewhole space.
 14. Camera system as defined in claim 1, characterized inthat the system comprises two adjacent semi-space recording cameras (1)directed in the same direction for the recording of a stereo image ofthe semi-space.